As a method of performing a collective expression analysis of a plurality of genes, an analysis method called a DNA chip method (DNA microarray method) is known. In this analysis method, a flat plate-shaped microarray in which for example, a plurality of DNA fragments are fixed inside through-holes at the central portion is immersed in a sample (liquid sample) containing expression genes and the like of a cell, which is marked by a fluorescent dye and the like and is a research target, to allow hybridization to be performed in order for complementary nucleic acids to be coupled, and a section in which a hybrid is formed is read by a detection device, thereby performing detection and quantity determination of the nucleic acids.
In the DNA chip method, when the hybridization is completed, before the detection and quantity determination of the nucleic acids, a washing process of washing a liquid sample adhering to the microarray with a wash buffer is performed.
In addition, in the DNA chip method, a microarray processing apparatus that performs the hybridization process and the washing process with respect to the microarray is used. In the microarray processing apparatus, a plurality of wells, which are formed in an elongated bottomed-hole shape having an upward opening, are arranged on an upper surface of the well plate. In each of the wells, a flat plate-shaped microarray, whose outer edge is held by a microarray holder having the same height as the depth of the well, is accommodated in an erected state, a liquid sample is injected into the well, and retention is performed for a predetermined time at a high temperature, thereby performing the hybridization process. Then, a wash buffer is injected into the well by using an injection nozzle while suctioning the liquid sample in the well, in which the microarray holder is accommodated, with a suction nozzle, thereby performing the washing process (Patent Document 1).